Actually what Kirk says is more like, "D'you really think that a guy as horny as me would hook up with someone who can only be convinced to do the Wild Money Sex once per seven years?"

Which makes a loophole big enough to fly a starship through, since it's not that Vulcan's don't have sex except when in Pon Farr, it's that they don't have the psychobiological fuck-or-fight imperative except then. I'm sure if they had a logical reason to screw other times they'd go ahead and do so.